Many flooring systems in residential and commercial buildings may comprise a floor supported by wood or steel joists. In some flooring systems the floor may comprise a finished floor that is disposed above a subfloor. In single-family and multi-family homes and small commercial buildings, the subfloor may comprise a poured concrete slab or be formed from wooden boards or panels that are laid over the joists. In some apartment buildings, larger commercial buildings and other steel-frame buildings, the subfloor may be a steel deck, precast concrete slabs or panels, or poured concrete.
The finished flooring provides a decorative, aesthetically pleasing floor surface. The finished flooring may be wood, such as wood planks, parquet flooring, laminate flooring, and wood-block flooring, or a resilient material, such as linoleum, asphalt tile, or vinyl or rubber tile or sheet, or carpeting.
Concrete typically comprises a combination of aggregate and a cement binder having a high water content. In some cases, the concrete may also include calcium chloride as a cure agent for accelerating curing of the concrete. After mixing, the cement hydrates and eventually hardens into a hard stone-like material. In many cases, the concrete retains a high moisture content that may slowly dissipate from within the concrete over a period of time. In some cases, concrete may also wick moisture from the surrounding environment, such as the ground, into the concrete. Moisture from within the concrete may dissipate upwardly through the concrete and come into contact with the floor.
Hardwood flooring and wood in general are hygroscopic materials. Liquid water and water vapor can enter wood which may cause it to swell and change its shape and size, potentially causing bubbling. If and when the water leaves the wood, the wood can shrink which may result in warp, the development of small cracks in the surface of the wood, twists, bows, or even develop cups or dips within each piece of wood flooring. In some cases, cracks in between pieces of wood may open up as the wood dries.
To help prevent moisture from contacting the finished flooring, it may be desirable to place a moisture barrier between the flooring and the subfloor. The moisture barrier may comprise a thin layer of film adhered to the surface of the concrete. In some applications an underlayment layer comprising a layer of polymeric film and a layer of polymeric foam, or a polyethylene film/foam laminate, is provided as an underlayment between the concrete subfloor and finish flooring formed of wood. The underlayment levels small irregularities in the top surface of the concrete, provides a small degree of resiliency to the floor system, and provides a vapor barrier to prevent moisture emanating from the concrete subfloor from attacking and deteriorating the finish flooring.
In addition to potential damage to wood in the flooring, water can also react with excess calcium chloride in the concrete. The reaction of water and calcium chloride is an exothermic reaction that generates heat that can dissipate into the underlayment material. The addition of heat in the polymeric material of either the film or foam layer can result in the cleavage of carbon-hydrogen bonds along the polymer chains and the generation of free radicals in the polymer. The thus generated free radicals can lead to further breakage of carbon bonds and the generation of additional free radicals. Overtime, these continued reactions can lead to degradation and failure of the underlayment material. For example, one or more portions of the underlayment material may prematurely fail, such as the formations of cracks and/or deterioration or delamination of the foam and film layers. Such degradation is particularly troublesome in flooring applications where the failure may not be easily discernable or easily remedied.
Thus, there exists a need for an improved floor underlayment which provides the cushioning, and floor leveling functions of the prior floor underlayments, but which also is resistant to degradation caused by excess heat so to avoid the disadvantages associated therewith.